One of the major challenges of proteomics is the sheer complexity of biomolecular samples, such as blood serum or cell extract. Typical blood samples could contain more than 10,000 different protein species, with concentrations varying over 9 orders of magnitude. Such diversity of proteins, as well as their huge concentration ranges, poses a formidable challenge for sample preparation in proteomics.
Conventional protein analysis techniques, based on multidimensional separation steps and mass spectrometry (MS), fall short because of the limited separation peak capacity (up to ˜3000) and dynamic range of detection (˜104). Microfluidic biomolecule analysis systems (so-called μTAS) hold promise for automated biomolecule processing. Various biomolecule separation and purification steps, as well as chemical reaction and amplification has been miniaturized on a microchip, demonstrating orders of magnitude faster sample separation and processing. In addition, microfluidic integration of two different separation steps into a multidimensional separation device has been demonstrated. However, most microfluidic separation and sample processing devices suffers from the critical issue of sample volume mismatch. Microfluidic devices are very efficient in handling and processing 1 pL˜1 nL of sample fluids, but most biomolecule samples are available or handled in a liquid volume larger than 1 μL. Therefore, microchip-based separation techniques often analyze only a small fraction of available samples, which significantly limits the overall detection sensitivity. In proteomics, this problem is exacerbated by the fact that information-rich signaling molecules (cytokines and biomarkers, e.g.) are present only in trace concentrations (nM˜pM range), and there is no signal amplification technique such as polymerase chain reaction (PCR) for proteins and peptides.
What is needed is an efficient sample concentrator, which can take a typical sample volume of microliters or more and concentrate molecules therein into a smaller volume so that such molecules can be separated and detected much more sensitively. Several strategies are currently available to provide sample preconcentration in liquid, including field-amplified sample stacking (FAS), isotachophoresis (ITP), electrokinetic trapping, micellar electrokinetic sweeping, chromatographic preconcentration, and membrane preconcentration. Many of these techniques are originally developed for capillary electrophoresis, and require special buffer arrangements and/or reagents. Efficiency of chromatographic and filtration-based preconcentration techniques depends on the hydrophobicity and the size of the target molecules. Electrokinetic trapping can be used for any charged biomolecule species, but generally requires nanoporous charge-selective membranes for the operation. Overall, the demonstrated concentration factors for the existing preconcentration schemes are limited to ˜1000, and their application to the integrated microsystems is difficult due to various operational constraints such as reagents and materials requirements.
On the other hand, removal of charged species and specifically salt is needed in microfluidic devices in order to produce pure fluids for synthesis and analysis. When the fluid is water, purified water is needed for drinking.
Fresh water is the vital resource for human life. However, population growth, enhanced living standards, along with expansion in industrial and agricultural activities are urging unprecedented demands on the clean water supplies all over the world. OECD and UN have reported that 0.35 billion people are suffering from the water shortage now in 25 countries, especially in the middle-east and Africa, but it will grow up to 3.9 billion people (⅔ of world population) in 52 countries by 2025. The shortage of fresh water is one of the acute challenges that the world is facing now and thus energy efficient desalination strategy can provide substantial answer for the water-crisis. Converting abundant seawater into fresh water can provide the solution to the worldwide water shortage problem, since about 97% of the total water resources on earth is seawater and only 0.5% of the total water resources are potable fresh water. Historically, distillation has been the method of choice for seawater desalination, in spite of its high capital and energy costs, suitable for middle-eastern countries where the fuel required for distillation is relatively inexpensive. The other standard approaches to seawater desalination are reverse osmosis (RO) and electro-dialysis (ED), with relatively good energy efficiencies (˜5 Wh/L for RO, and 10˜25 Wh/L for ED). The RO process requires the generation of large pressure in order to overcome seawater osmotic pressure (˜27 times of atmospheric pressure) across the semi-permeable membranes used. The ED process utilizes electrical currents to move ions selectively through perm-selective membrane, leaving pure water behind. The three seawater desalination techniques mentioned above require large scale systems with significant power consumption and other large scale infrastructure considerations which critically increase the operation cost of such systems. These features render the methods unsuitable for disaster-stricken areas or underdeveloped countries.
This presents a significant global challenge, since the areas affected by acute water shortage are often in the poorest, most underdeveloped countries. Lack of clean water also presents significant health, energy and economic challenges to the population in these countries. In this sense, small scale or portable seawater desalination systems with low power consumption and high throughput would be very useful in many important government, civilian and military needs, including humanitarian operations in disaster-stricken areas or resource-limited settings. Another significant challenge in seawater desalination is detecting and removing micro/macro particles, bacteria, and other pathogens contained in the source water. These particles and microorganisms cause membrane fouling, which is a major issue both for RO and ED systems. The forward osmosis process (extracting the seawater into even saltier liquid, followed by reverse osmosis) was utilized for filtration in a seawater desalination process, but its operation suffers from high costs due to additional energy consumption.